ANASEN - Array for Nuclear Astrophysics Studies with Exotic Nuclei

Silicon-strip detector array backed with 2-cm-thick CsIGas proportional counter for proton-tracking capabilitySupported by NSF MRI Program

Here: 1) Nuclear Structure studies of light nuclei 2) Nuclear Astrophysics measurements

To improve understanding of light rare isotopes and (p,) and (,p) rates that are important in the p/rp processes

Flexible, large-area charged-particle detector array targeting (,p) reactions, proton scattering, and transfer reactions using the ReA3 facility at the NSCL and RESOLUT at FSU Active Target

Jeff Blackmon (LSU), Grigory Rogachev (FSU),

Ingo Wiedenhoever (FSU) and Ed Zganjar (LSU)

ANASEN

3 Rings of 12 Super-X3 silicon-strip detectors backed w/ 2cm thick CsI

Annular silicon-strip array

RIB

Anode wires of cylindrical gas proportional counter

Silicon Strip Detectors

X3 detectors constructed for ORRUBA by Micron Semiconductor4 resistive strips (10mm X 75mm) S.D. Pain et al., NIMB261 (2007) 1122.

Ep

Forward angle detectors currently under design18cm outer diameter in 4 quadrants (6” Si)Minimal (~1mm) PC board on outer radiusPin out and mounting along radial direction8cm ID design for use with PC

x < 1 mmE < 100 keV

“Super-X3” version40x19 mm Ohmic segmentation

First 12 detectors ordered

1 mm thick detectors

MicronQQQ2 design

Proton-Resonant Scattering with ANASEN

Thick, active target allows simultaneous measurement of multiple resonances

Proton-depth tracking allows distinction between elastic and inelastic excitations

Same depth,different Ep ?

Beam slows downin target gas, scans over Resonanceenergies

p

Beam View

Structure of 8B

P. Navratil et al., PRC 73, 065801 (2006)

http://cosmo.volya.netD. Morris & A. Volya

Study of light exotic nuclei through resonance reactions with RNB’sRNB8, 2009

Structure of 8B

G.V. Rogachev et al., Phys. Rev. C64 (2001) 061601(R)

3+

2-

7Be+p

Dominant configuration for the “missing” states is 7Be*(1/2-)+p. Should be observed in inelastic scattering.D. Halderson, PRC 69, 014609 (2004)

Study of light exotic nuclei through resonance reactions with RNB’sRNB8, 2009

RF-Resonator

Magnetic Spectrograph

Target Position

RF-Resonator

Magnetic SpectrographSolenoid 2

Solenoid 1

Mass selectionslits Production

target

In-flight production of radioactive beams in inverse kinematics

Combination of Superconducting RF-Resonator with high acceptance magnetic Spectrograph to create mass spectrometer

RESOLUT: a new radioactive beam facility at John D. Fox Superconducting Accelerator Lab. at Florida State University

Hybrid (thick/thin) target technique

Target is thick enough for 7Be to lose significant fraction of it’s energy.

But thin enough for 7Be recoils to make it out of the target.

7Be

p

7Be

CH2

E1 E3

RESOLUT beam composition: 75% of 7Be, 25% of 7Li

Study of light exotic nuclei through resonance reactions with RNB’sRNB8, 2009

7Li(p,n)7Be

I7Be=2x105 pps

Study of light exotic nuclei through resonance reactions with RNB’sRNB8, 2009

Excitation function of inelastic p+7Be scattering compared to R-matrix calculations with no new states in 8B.Elastic

Inelastic

Inelastic

140o

U. Greife, et al., NIM B 261 (2007) 1089

Study of light exotic nuclei through resonance reactions with RNB’sRNB8, 2009

7Be(p,p) 148o

7Be(p,p) 140o

7Be(p,p) 132o

7Be(p,p’)7Be* 146o

7Be(p,p’)7Be* 138o

7Be(p,p’)7Be* 130o

Red curve is an R-matrix fit with the following resonances:

1+ - 0.77 MeV; known [1]0+ - 1.8 MeV; new3+ - 2.32 MeV; known [1]2+ - 2.4 MeV; new2- - 3.5 MeV; known [2,3]1+ - ~3.5 MeV; new

(,p) with ANASEN as active target

Top View

+HV

p

p

Beam View

Chamber filled with ~ 200-400 Torr He gas Beam enters through ~ 2m Ti foil

Protons produced with energies from few ~20 MeV in extreme cases 4He(18Ne,p): Ep~3-11 MeV For 10 MeV protons, E ~ 5 keV in PC region 105 e Resistive wire good determination of position in PC

Example: 36 MeV 18Ne22 MeV 18Ne after window (4 MeVcm)

Elab~0.68 MeV/cm in 200 Torr

Ecm~120 keV/cm

(,p) - count rates, resolution, issues

Entire excitation function measured with 1 bombarding energy Should be able to measure (a,p) cross section over a significant fraction of

the Gamow window - though more difficult for heavier Z

Ecm can be reconstructed with good (<100 keVcm) resolution, but

o More difficult for forward/backward angles

o Dependent on emittance of beam

o Thickness required of PC for accurate position reconstuction?

o Leakage of charge from high ionization region of beam into PC

Proton scattering and (p,) with ANASEN

Our understanding of (p,) and (,p) reactions can be improved by studying nuclear structure via• proton elastic scattering• proton inelastic scattering• (p,) reactions

p-process

Red = Most interesting cases

Neutron-Detector Development: 6Li-Glass Sandwich

(d,n) in inverse kinematics:

Detect low-energy, 30-100 keV neutrons in “backward” directions γ-p branching ratios and angular distributions

Plan: use 6Li-glass scintillator-stack (5 cm depth=10% efficient.)

25Al p25Al

n

15 cm

26Si

CD2